The present invention relates to the field of digital signal processing. More particularly, the present invention relates to specific digital signal processing algorithms for reducing the artifacts associated with still frame display and video capture of interlaced video.
Most, if not all, analog broadcast video, and some digital video, is created and transmitted in interlaced video format. FIG. 1 illustrates the interlaced video format. xe2x80x9cInterlacedxe2x80x9d means that an image (i.e., a picture or a frame), is broken up into two fields, usually referred to as xe2x80x9cfield 1xe2x80x9d and xe2x80x9cfield 2xe2x80x9d or xe2x80x9codd fieldxe2x80x9d and xe2x80x9ceven field.xe2x80x9d Each field contains one-half of the lines of video information (e.g., analog waveform or digital pixels) which make up the full image. Field one is displayed first on the screen, and contains one-half of the video image lines (e.g., the odd numbered lines) in the vertical direction. Field two is then displayed, containing the remaining one-half of the lines of the image (e.g., the even numbered lines). The lines of field two are displayed in-between the lines of field one. Together, the lines of field one and field two make up the entire picture or frame. In live video construction, the second field is time displaced from the first field by {fraction (1/60)} of a second when a frame rate of 30 frames per second is used. Therefore, motion in the video source will be present in the displayed picture between the two fields.
In advanced set-top terminals used, e.g., for receiving television signals in a cable or satellite television system, video still frame and video capture are important features. There are several potential constraints and trouble spots associated with the implementation and resulting image quality with both still frame display and video capture features.
Video still frame display means that the user can initiate the set-top terminal to stop displaying continuous video, and display the presently displayed single image continuously. This feature is similar to the pause feature on a VCR. Field to field motion and significant brightness changes between adjacent lines of the two fields are significant problems for image quality when implementing a video still frame display feature. The still frame captured and being displayed will be presented as field one followed by field two, repeated continuously. If there is motion between field one and field two, this motion will cause a jittering effect when continuously displayed as a still frame. For instance, if the still frame contains motion in a person""s hand, the resulting still display will show the hand moving back and forth at a 60 Hertz rate. If the still frame contained a hard scene change, the resulting still image display would be almost unrecognizable with a great deal of 60 Hertz flicker. In addition, significant brightness changes between adjacent lines of the two fields will result in a flickering effect.
Video capture means that the user can acquire an image from live video. The captured image can be re-formatted as any standard type image format, such as a computer file in one of the standard .tif, .bmp, or jpg formats, etc., and is usually de-interlaced in the process. This captured image can then be utilized in various ways (e.g., attached to an outgoing e-mail). If both fields are used for the video capture feature, the problem of inter-field motion is encountered. This is due to the second field being time displaced from the first field during construction and display. Motion occurring between the two fields will result in a blurred image, where more motion causes a blurrier captured image. If the motion present between fields is severe enough, for instance a hard scene change, the resulting captured image can be almost unrecognizable.
Due to the motion issue, and also to possibly save memory space, a single field can be utilized for video capture. However, as illustrated in FIG. 4, if just one of the two fields is utilized to make the image, the resulting image (e.g., first field image 210) will be squashed in the vertical direction, with adverse effects such as turning a circle into an egg.
It would be advantageous to provide methods and apparatus which compensate for the artifacts associated with still frame display and video capture techniques of interlaced video, including flicker and blurring artifacts. It would be further advantageous to provide for the reduction of such artifacts using specific algorithms.
The methods and apparatus of the present invention provide the foregoing and other advantages.
The present invention relates to methods and apparatus for reducing the artifacts associated with still frame display and video capture of interlaced video. A receiver is provided for receiving an interlaced video signal having an image frame with a first field and a second field. A motion detector for detecting whether motion is present between the first and second fields is provided. A field store memory is provided for storing the first field for further processing in the event motion is detected. A processor processes the stored first field to provide an image frame with reduced artifacts. Various processing techniques are provided to generate the image frame from the first field, without the need to duplicate the first field for use as the second field. Additionally both fields can be stored and processed to provide the reduced artifact image. An image store memory is provided for storing the image frame. In the event no motion is detected, the first field and the second field are both stored to provide the image frame. The stored image frame can then be continuously displayed to provide a still frame display, or can be captured for subsequent use (i.e., transferred to writeable media and reformatted).